Certain devices such as wafer defect scanners, laser printers, document scanners, projectors and the like make use of a narrow collimated laser beam that usually scans across a flat surface along a straight line path. A typical optical scanning system for this purpose employs a tilting flat mirror to deflect the beam. The tilting micro-mirror serves as a central element in many Micro Electro Mechanical Systems (“MEMS”) devices and/or Micro Opto Electro Mechanical Systems (“MOEMS”) devices. For the sake of convenience, these devices (i.e. MEMS and/or MOEMS) will be referred to herein as “MEMS” devices.
Many of these MEMS devices comprise two types of electro-static mirrors: in-plane mirrors and staggered mirrors. In-plane mirrors are usually driven at a resonance frequency. The stator and the rotor of in-plane mirrors are fabricated on a single layer, and the mirror's driving pulse is usually of a rectangular type signal. Staggered mirrors are typically comprised of two different layers: one that includes the stator and a second that includes the rotor. In some embodiments, however, such as where the stator or the rotor is tilted permanently after manufacturing, a single layer may be used for both the stator and the rotor. The staggered mirrors may operate at their resonance frequency or at lower frequencies down to, and including, DC.
Traditional driving control circuitry for MEMS mirror devices requires complex processing and use of A/D converters, amplifiers, and filters for monitoring the mirror. Moreover, changing the laser light power causes a change in mirror resonance frequency that traditional control algorithms are slow to detect and accommodate. Therefore, a need exists for a simplified control system that addresses the deficiencies of traditional MEMS mirror driving control circuitry.